1. Field of the Invention
The present invention relates to the field of optoelectronic components and more particularly to an improved housing design for a radiation sending and/or receiving device. Such device may comprise one or more optoelectronic chips, which are generally mounted on a chip supporting part of an electrical lead frame running through a base body. Common applications for such chips may include light emitting diodes (LED).
2. Description of Related Art
Housings for radiation sending and/or receiving devices are generally well known in the art. An example of prior art housings is set out in an article “Siemens-SMT-TOP-LED-LED's for Surface Mounting”, Siemens Components XXVI (1991), Nos. 4-5, pages 147 to 149. This article is herein incorporated by reference. The article discusses the state of the art, as of 1991, of surface mounted TOP LED's. A side by side comparison of TOP and radial LEDs is set out in FIG. 4 of the article. A perspective view of a TOP LED is shown in FIG. 1 of the article. The figure depicts a rounded portion at the top of the LED along with a side protruding conductor strip or electrode. FIG. 2, of the article sets or depicts a cross section of the LED suggested in FIG. 1. Herein, a punched conductor strip 1 is encased in a thermoplastic package 2. The package 2 includes a top and bottom portion, the bottom portion being surrounded by the protruding conductor strip ends. The top portion of the package includes slanted, reflective and opposing sidewalls 3. The sidewalls form a circular opening in the top portion of the package within which is mounted semiconductor chip 4. The chip is consecutively mounted on a first portion of the punched conductor strip and further electronically connected (via a bonding wire) with the second portion of the punched conductor strip. The circular opening created by the sidewalls 3 is filled with a transparent epoxy resin. The resin is chosen such that the resin and package material are carefully balanced such that peak thermal stress will not cause mechanical damage. No such consideration is given to the selection of conductor strip 1 material. In operation, where, for example, the chip emits radiation, such radiation is reflected by the side walls 3 and emitted upwards through the window. Returning to FIG. 4 of the article, the SMT LED is mounted within a case and optically coupled to a light guide to the front panel of the case. Application of LED technology includes visual displays both in harsh environments, such as engine compartments, and non-harsh environments, such as home displays.
An embodiment resembling the TOP LED is set out in the instant FIG. 4. Herein, a housing 109 is depicted being generally made of a synthetic reflective material, such as a highly diffusive thermoplastic material as known to one skilled in the art. In the housing 109, a radiation emitting semiconductor chip 101 is mounted on a flat chip carrier portion 102 of a flat surface area of a punched metallic conductor 103. The conductor 103 is punched into two opposing, electrically isolated first and second portions, 103a and 103b, respectively, with chip 101 being mounted on the first portion 103a. The first portion further ends in an external connector 104. Portion 104 facilitates transmission of electrical signals with chip 101, from an external apparatus (not shown), via first portion 103a and carrier portion 102. Chip 101, via bonded wire 111, is electrically connected to second portion 103b of the metal carrier frame. In particular, wire 111 is bonded at area 107 of the second portion 103b. The second portion further ends in external connector 105 which facilitates communication of electrical signals with chip 101, from an external apparatus (not shown) via area 107 of second portion 103b and the connecting wire. Housing 109 further accommodates a transparent window 110 located above and around semiconductor chip 101. The window may be made of any appropriate synthetic material known to one skilled in the art. A top portion of the window 110 is coplanar with a top surface of housing 109. The side and bottom surfaces of window 110 are defined by cooperation of side wall 120 surfaces 112 and carrier frame 103. Sidewall surfaces 112 are angled with respect to frame 103. Side wall surfaces 112 and portions of carrier frame 103 that directly abut window 110 may have reflective properties for select or all radiation present within window 110. Semiconductor 101 may be radiation emissive and/or receptive.
A drawback with the above discussed arrangements, as briefly alluded to in the prior art reference, stems from the delamination of the window 110 carrier frame 103. Such delaminating may result from temperature variations in the housing's operating environment, such as proximate to an automobile engine or manufacturing (e.g. soldering) requirements. The temperature variations effect the thermal coefficients of the window, side walls and carrier frame causing dimensional changes in each at possibly differing rates. By way of example, frame 103 may be metal and window 110 may be a transparent epoxy resin. Hence, as a result of temperature fluctuations, the window 110 often separates from frame 103. Such gaps result in radiation absorption and/or internal reflections thereby diminishing the amount of radiation being emitted from or incident to chip 101. Hence the operating efficiency of the entire housing is effected. Furthermore, the gap can continue between carrier frame and window to sidewalls 120 starting from the gap between carrier frame 103 and window 110 thereby opening the housing up to moisture penetration which will damage the chip and accelerate delimitation.
U.S. Pat. No. 5,985,696 sets out application of a semiconductor chip in a rounded LED. The reference discloses a method for producing optoelectric semiconductor components wherein the chip carrier is supported by a plastic base and electrodes run through the base. A lens is further mounted above the chip. A cap is form fitted to a holder and attached with the base. The plastic base is one of many arranged successively in a chip carrier strip. The base is injection molded and the component is separated from the chip carrier strip only after the base is produced, the chip is attached and bonded to the electrodes.
U.S. Pat. No. 6,066,861 sets out an arrangement for a white light emitted diode. The arrangement includes an inorganic luminous substance pigment powder with luminous substance pigments dispersed in a transparent epoxy casting resin. The material is spaced proximate to a semiconductor radiation source such that the material luminesces, thereby converting the source radiation into a second wavelength. FIG. 3 sets out an embodiment whereby angled sidewalls and a base cooperate to form a bound area for the luminescing material.
German patent DE 19536454 discloses a semiconductor chip mounted on a lead frame and housed in a recess of a component base. A reflective layer is coated on the lead frame so as to reflect radiation emitting from the chip. Angled sidewalls further cooperate with a planar base to form the boundaries of the window.